The long-range objective of the proposed research is to develop the experimental and theoretical foundation needed to extend the use of ultrasound for the non-invasive identification and differentiation of normal, ischemic, and scarred myocardium. The hypotheses underlying this research are that pathological changes occurring in myocardium undergoing infarction alter the physical (i.e., mechanical) properties of the tissue and that these alterations can be measured and quantitated to provide an estimate of the extent of myocardial injury using an index based on the frequency dependence of the attenuation of ultrasound. We propose a series of experiments to study recent and remote infarcts in which results of ultrasonic measurements are compared with results of independent measurements of tissue properties. Specifically, we propose to (i) correlate the results of ultrasonic attenuation measurements with results of a biochemical assay for tissue content of collagen based on hydroxyproline for dogs studied 2 to 8 weeks following coronary occlusion, (ii) conduct experiments designed to determine the effect of myocardial tissue water content on the ultrasonic attenuatioon, (iii) determine what fraction of the ultrasonic attenuation observed in normal, edematous, and scarred myocardium can be accounted for on the basis of theoretical models that have been proposed to account for the propagation of ultrasound in soft tissue, (iv) develop and validate methods for measuring an index based on attenuation using reflected ultrasound, (v) approach methods suitable for investigations in vivo utilizing techniques for the study of open-chest dogs which may be applicable to the intact, conscious animal.